The present invention relates to devices, methods and apparatus for performing chemical separations, and, in particular, for performing chromatography. The term “chromatography” refers to the separation of compounds based on differences in affinity or absorbance. In chromatography, compounds are held in a solution of a gas, liquid or supercritical fluid. The solution in which the compound is dissolved is known as the “solvent”. The dissolved compounds exhibit differences in absorbance or affinity to a media that is not dissolved in the solvent. This media is held in place, stationary to the flow of a solution holding the dissolved compounds. This media is commonly a solid phase material.
Chromatography is a common research tool and can be used to process samples for analysis by various detection techniques. Chromatography is used to grossly separate many compounds from a sample, as an extraction technique. Chromatography can also be utilized as a fine separation technique in which subtle changes in molecular structure and function alter the affinity of the compounds to an immobilized media. Closely related compounds, for example drugs and drug metabolites, can be effectively separated.
Chromatography is performed in open systems or closed systems. In open systems chromatography is performed without significant pressure differentials. Examples of devices used in an open type system are well-like devices, such as ninety-six well extraction plates.
An example of a closed system is high performance or high pressure liquid chromatography (HPLC). Closed chromatography is normally performed with columns and cartridges through which solutions are pumped under pressure. The columns and cartridges typically have a packing of an immobilized media, such as silica or polymeric particles, to which compounds adsorb. A sample is flowed through the media and compounds in the sample adsorb to the media. This paper will make no distinction between a column and cartridge, and will use the term “column” to mean column or cartridge unless specifically stated otherwise. Analytical columns are columns made with fine tolerances for effecting reproducible qualitative and quantitative separations of closely related compounds. Columns, and analytical columns, in particular, are expensive.
The initial flowing of sample onto the media is called “loading”. Removing the potential compounds of interest is known as “eluting”. Elution is often performed by changing the solvent composition. Preparing the media to receive the sample is known as “conditioning”. Ensuring the prior sample is removed from the media, to allow a next sample to be loaded on the media is known as “washing”.
The term “sample” will be used to denote any material that is received for processing. In clinical settings, a sample may comprise a biological fluid or tissue. The term “analyte” will be used to mean a composition of interest, potentially present in a sample. Samples and solvents may contain particulates, globules and other materials that are not of analytical or diagnostic interest. For simplicity, this paper will refer to all such particulates, globules and materials as particulates. These particulates may accumulate and reduce flow in columns such that the column no longer is useful.
Columns are normally in fluid communication with a detector. As used in this paper, the term “detector” refers to a device that produces a signal in response to the presence or absence of a composition. A typical detector is in the nature of, by way of example, without limitation, mass spectrometers, optical sensors, such Raman detectors, light scattering detectors, fluorescent detectors, chemi-luminescent detectors, light absorbance detectors, light refraction detectors, electrochemical detectors, viscosity detectors, nuclear magnetic resonance detectors.
HPLC is normally performed at pressure of up to 5,000 pounds per square inch (psi). However, there is a desire to operate at pressures above 5,000 psi, including pressures in the extreme pressure region of 5,000 psi up to 15,000 psi. At such elevated pressures and with higher flow rates associated with such pressures, the size of columns and conduits to effect fluid communication between fluidic elements is generally reduced. With the smaller size, columns are more sensitive to particulates and pressure pulsation. As used herein, pressure pulsation refers to the changes in pressure associated with pump, valve and other mechanical inefficiencies and errors.
Guard columns are used to protect and extend the useful life of analytical columns. However, the use of guard columns to protect other columns, such as an analytical column, often entails substantial additional conduits and tubing. The additional tubing and conduits adds to the potential of leaks and contributes to band spreading due to the effects of the walls of the conduits and tubes, and decreases the responsiveness of the system to changes in fluids during elution process or washing processes.
Thus, there is a need for devices, methods and apparatus which function to protect a column and detector sensitive to the effects of particulates and pressure pulsations and ripples in a high pressure and extreme high-pressure environment.